The present invention relates to a laser transmitter and, more particularly, to a laser transmitter having a simple, quickly implemented arrangement for correcting for initial misalignment of the beam or beams produced by the laser transmitter. The present invention is particularly well suited for correction of optical errors in transmitters of the type that produce one or more stationary reference beams.
Simple transmitters of this type have been used in construction to project one, two, three, or more beams of visible light for alignment purposes. One such transmitter is shown in U.S. Pat. No. 3,897,637, issued Aug. 5, 1975 to Genho. A beam from a laser source is collimated and then split into three beams that precisely define a three-dimensional reference coordinate system.
A similar transmitter is shown in U.S. Pat. No. 5,500,524, issued Mar. 10, 1996, to Rando. In the Rando patent, a beam from a laser diode is split by appropriate optics into three orthogonal beams. Compact battery-operated laser projectors of this type have found wide use in the construction industry in performing alignment operations. For example, a visible beam of light projects a straight line in space, and this visible beam can be used to locate building references. A leveled or plumb beam of light can be used to set the level or plumb directions of building elements such as floors, walls, and columns. In many applications a small-diameter visible laser beam replaces a string line. The beam strikes an object producing a small spot of light. The center of the spot can then be marked with a pencil as needed.
Typically, the transmitters or projectors of this type use a single diode light source and divide or split the light beam with optics. For example in U.S. Pat. No. 5,144,487, issued Sep. 1, 1992, to Hersey, two co-linear beams are generated using a beam splitter and a mirror. Transmitters of this type require precise alignment of optical elements to achieve the desired level of accuracy.
Several approaches to adjusting or aligning the output beam of a laser projector or transmitter are shown in U.S. Pat. No. 5,959,789, issued Sep. 28, 1999, to Rando. In FIG. 3 of the Rando patent, two optical wedges or prisms are shown as mounted in the output path of a beam. The two wedges can be rotated independently about an axis aligned with the laser beam. The wedges refract the beam in two directions and, if properly set, can effect varying amounts of beam alignment correction in any direction. The Rando patent also shows using a single optical element comprising a low magnification telescope that can be rotated in a semi-spherical seat to steer a beam in a desired direction and correct beam misalignment. The Rando patent teaches adhesively affixing the low magnification telescope in place when the desired correction is obtained. While effecting correction, the mounting and the telescope are somewhat complicated mechanically. A need exists for a simple, inexpensive way to compensate a reference beam transmitter for slight errors introduced during manufacture and assembly so that the final transmitter is inexpensive, rugged, and accurate.